usb gadget: USB_GADGET_VBUS_DRAW Kconfig option

Offer a "how much VBUS power to request" configuration option
for USB gadgets that aren't using board-specific customization
of their gadget or (composite) configuration drivers.

Also remove a couple pointless "depends on USB_GADGET" bits
from the Kconfig text; booleans inside an "if USB_GADGET" will
already have that dependency.

Based on a patch from Justin Clacherty.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Justin Clacherty <justin@redfish-group.com>
Tested-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/gadget/file_storage.c b/drivers/usb/gadget/file_storage.c
index e0f616f..c4e62a6 100644
--- a/drivers/usb/gadget/file_storage.c
+++ b/drivers/usb/gadget/file_storage.c
@@ -851,7 +851,7 @@
 	.bConfigurationValue =	CONFIG_VALUE,
 	.iConfiguration =	STRING_CONFIG,
 	.bmAttributes =		USB_CONFIG_ATT_ONE | USB_CONFIG_ATT_SELFPOWER,
-	.bMaxPower =		1,	// self-powered
+	.bMaxPower =		CONFIG_USB_GADGET_VBUS_DRAW / 2,
 };
 
 static struct usb_otg_descriptor